1 Introduction
Disc harrows began to be made and used in many countries in the 1870s. The production and use of disc harrows in China developed from the promotion of animal disc harrows in the early 1950s. In the 1960s, 41 light disc harrows, 20 notched disc harrows and 24 offset harrows were manufactured successively. A series of disc harrows for 18 ~ 55 kW tractors were developed in the 1970s, with more than ten types of tractive, suspended and semi-suspended models.
2 Working components
It is a rake group of concave disk fixed distance series mounted on the shaft. The concave surface of the disk is generally spherical, and some countries also use conical surface. There are two kinds of disc: whole edge edge and notched edge. The former is easy to manufacture and easy to grind. The latter is good for cutting up clods and stubble weeds, and is often used on heavy harrows for clay soil tillage. Rake size has been standardized in various countries, and there are international standards. The rake is generally made of wear-resistant 65Mn steel, or low carbon martensitic B5 steel. In the United States, harrows have been made from steel plates rolled in cross rolls since the 1940s. The center hole of the disc harrow piece is generally square hole, separated by the intertube, the harrow piece and intertube are set together on the square shaft and locked with nuts to become the harrow group. When working, the cutting edge plane of the disk is perpendicular to the ground and becomes a deflection Angle with the direction of advance. Each harrow group is supported by bearings on the rack. During operation, under the action of tractor pulling force and soil reaction force, each harrow piece of the harrow group rolls with the same square shaft. The blade of the rake is inserted into the soil under the action of the rake's own gravity, cutting off grass roots or crop stubble, shredding the soil strip and causing it to rise slightly along the concave surface of the rake and then topple over, providing soil and cover. The declination Angle of rake group can be adjusted, the adjustment range is generally 0° ~ 30°, and the usual declination Angle is 10° ~ 25°. Increasing the deflection Angle can increase the depth of the rake and the effect of turning and breaking the soil, and the resistance will also increase.
3 Complete machine structure
Disc harrow is composed of harrow frame, harrow group, traction or suspension device, deflection adjustment mechanism and so on. In order to increase the depth of the soil, some light and small harrows are equipped with a weight box on the harrow rack. The disk harrows used in production in the 1980s have a large weight distribution on each disc and sufficient ability to penetrate the earth, so it is unnecessary to add counterweight and adjust the deflection Angle. When the harrow group is installed, its deflection Angle is fixed in the * position. When shallow ploughing is required, the depth is limited by wheels controlled by hydraulic cylinders.
The number of harrow groups before and after the broad harrow can be 8 groups, and the number of harrow pieces can reach 104. The single-chip heavy harrow weighs 75 kg. The width of the light harrow is about 9 meters. For harrows with a width of more than 4 meters, the two wing harrows can be folded up or brought together for lateral traction.
Traction harrow is usually equipped with a device that can automatically adjust the transportation state and manually fine-tune the joint in the working state on the traction device (Figure 6). With the help of the lifting of the wheel and the linkage of the rod, the harrow frame is always kept level
